1. Field of the Invention
The present invention relates to a process for producing hydroxy-functional polyurethane carbonates, to the resulting hydroxy-functional polyurethane carbonates and to their use as a binder component for polyurethane compositions, especially coating compositions.
2. Description of the Prior Art
Homopolymeric or copolymeric, hydroxy-functional, aliphatic polycarbonates are known. They are used in the field of high-quality polyurethane plastics and polyurethane coatings because of their high resistance to hydrolysis. They are generally produced from diols which are not vicinal diols, by reaction with a diaryl carbonate (DE-A 1,915,908) or a dialkyl carbonate (DE-A 2,555,805). Of the diols described in the literature, only those which are exclusively or predominantly based on 1,6-hexanediol have previously achieved major commercial importance.
Homopolymeric polycarbonates based on C4-C12 diols are crystalline solids having a melting point between 30 and 60xc2x0 C., depending upon their molecular weight (H. Schnell in xe2x80x9cChemistry and Physics of Polycarbonatesxe2x80x9d, J. Wiley and Sons, 1964, page 15). Copolymeric polycarbonates, such as those described in U.S. Pat. No. 4,553,729, for example, are in fact liquid at room temperature, but their viscosity is so high that they can only be used with difficulty for the production of polyurethane plastics and polyurethane coatings.
Polyester polycarbonates based on caprolactone (DE-A 1,770,245) or low molecular weight adipic acid polyesters (EP-A 364,052) exhibit a reduced tendency towards crystallization and a lower viscosity, but the resistance to hydrolysis of polyurethane plastics and polyurethane coatings based on these diols is reduced.
Polyether polycarbonates, such as those described in DE-A 2,221,751 or in EP-A 292,772 are more hydrophilic, and have an inferior resistance to weathering due to their ether groups.
EP-A 624,614 teaches the production of polyurethane polycarbonates by the reaction of polycarbonates with diamines. The products obtained contain free terminal amino groups and are wax-like at room temperature when pure polycarbonates are used. Despite this disadvantage, these products are valuable starting materials for the production of polyurethanes. However, these products are unsuitable as binders or binder components in coating compositions.
An object of the present invention is to develop polymers containing hydroxy-functional carbonate groups which do not exhibit the said disadvantages of the prior art.
It has now surprisingly been found that low-viscosity, hydroxy-functional polyurethane polycarbonates which are stable towards crystallization are produced when polymers containing aliphatic carbonate groups are reacted with certain amino alcohols.
The present invention relates to a process for preparing hydroxy-functional polyurethane carbonates by reacting
a) a dihydroxy- or higher hydroxy-functional polymer having a number average molecular weight of 500 to 100,000 and containing aliphatic carbonate groups and optionally ester groups with
b) compounds containing at least one primary or secondary amino group and at least one hydroxy group to form urethane groups, wherein components a) and b) are present in amounts which correspond to a molar ratio of carbonate and ester groups of component a) to primary and secondary amino groups of component b) of greater than 1:1 to 20:1.
The present invention also relates to the hydroxy-functional polyurethane carbonates obtained by this process and to their use as a binder component in polyurethane compositions, especially coating compositions.
The hydroxy-functional, aliphatic polymers containing carbonate groups which are suitable for use as component a) are known in the art. All dihydroxy- or higher hydroxy-functional aliphatic homopolymeric or copolymeric polycarbonates can be used. Polycarbonates which contain other groups in addition to carbonate groups, such as polyester polycarbonates or polyether polycarbonates, may also be used. Dihydroxy, aliphatic, homopolymeric or copolymeric polycarbonates are preferably used.
The number average molecular weight (Mn, which may be calculated from the hydroxyl group content and hydroxyl functionality) of the polymers which contain carbonate groups and which can be used as component a) is 500 to 100,000, preferably 500 to 10,000 and more preferably 1000 to 5000.
Component b) is selected from organic compounds which contain at least one primary or secondary amino group and at least one hydroxyl group per molecule. Examples include ethanolamine, 1-amino-2-propanol, 2-amino-1-propanol, 3-amino-1-propanol, 2-amino-1-butanol, 4-amino-1-butanol, 2-amino-2-methyl-1-propanol, 2-tert.-butylaminoethanol, 2-amino-3-methyl-butanol, methylamino-ethanol, 2-(ethylamino)-ethanol, 2-(2-aminoethoxy)-ethanol, 2-(2-aminoethylamino)-ethanol, 2-((3-amino-propyl)-methylamino)-ethanol, diethanol-amine, 2-amino-2-methyl-1,3-propanediol, 3-(aminomethyl)-1,2-propanediol, 3-amino-1,2-propanediol, 1,1xe2x80x2-iminodi-2-propanol, 2-amino-2-hydroxymethyl-1,3-propanediol, 3-piperidinol, 4-piperidinol, 2,2,6,6-tetramethyl-4-piperidinol, 2-aminobenzyl alcohol, 3-aminobenzyl alcohol, 2-(benzylamino)-ethanol, 2-anilino-ethanol, 2-amino-3-phenyl-propanol, 2-amino-1-phenyl-1,3-propanediol and mixtures thereof.
The compounds which are preferably used are aliphatic compounds containing a primary or secondary amino group and at least one hydroxy group and mixtures of these compounds. Especially preferred are aliphatic compounds containing a secondary amino group and at least one hydroxy group, such as methylamino-ethanol, diethanolamine, 1,1xe2x80x2-iminodi-2-propanol and mixtures of these compounds.
Components a) and b) are used in amounts which correspond to a molar ratio of the carbonate groups and optionally ester groups of component a) to primary and secondary amino groups of component b) greater than 1:1 to 20:1, preferably 1.1:1 to 10:1 and more preferably 1.1:1 to 3:1.
The process according to the invention is generally conducted in the absence of solvent by mixing components a) and b) with each other. The reaction is conducted at a temperature of 20 to 180xc2x0 C., preferably 40 to 140xc2x0 C.
In order to speed up the reaction of components a) and b) and/or to reduce the temperature of reaction, catalysts may optionally be used. Examples include triethylamine; tributylamine; 1,4-diazabicyclo-(2,2,2)-octane; N,N-dimethyl-benzylamine; 2-methylimidazole; Mannich bases; tetraalkyl-ammonium hydroxides; alkali hydroxides such as lithium hydroxide or sodium hydroxide; alkali phenolates; alkali alcoholates such as methylates or ethylates of lithium, sodium or potassium; the catalysts described in EP-A 624,614 which contain mixtures of alkali alcoholates and alkyl formates such as methyl formate or ethyl formate; tin compounds such as tin(II) octoate or dibutyltin oxide; and mixtures thereof.
The reaction is preferably conducted without a catalyst or with strongly basic catalysts such as alkali alcoholates.
When basic catalysts are used, they can optionally be neutralized after completion of the reaction with inorganic or organic acids, such as sulphuric acid, acetic acid, methanesulphonic acid and p-toluene sulphonic acid.
The progress of the reaction according to the invention can be determined by IR analysis (decrease of the amine bands at about 1590 cmxe2x88x921) or by the decrease in the amine number. The reaction is generally carried out until the amine number is less than 5.
The hydroxy-functional polyurethane carbonates obtained according to the invention are valuable binder components for polyurethane compositions, especially coating compositions, wherein they may optionally be used in combination with known cross-linkers such as polyisocyanate resins.